Medical care for the population of Olmsted County, Minnesota, is almost entirely provided by the Mayo Clinic and the Olmsted Medical Group and their affiliated hospitals. The records of these institutions and other outside sources have been assembled into a single diagnostic retrieval system and provide a unique resource for population-based epidemiologic studies of serious chronic disease. Under the Rochester Epidemiologic Program Project (GM 14231), we are now completing a Coronary Heart Disease (CHD) study which will establish the local incidence rates for first manifestations of CHD under the subgroups angina pectoris (AP), myocardial infarction (MI), and sudden unexpected death (SUD) over the period 1950-1975. In that study we have 100% follow-up for five years nd 99.6% follow-up to 1/1/76, a 60% autopsy rate in the AP and MI groups, and 86% in the SUD group. Preliminary date indicate only minor changes in CHD incidence, improved survivorship in AP, and during the last ten years a dramatic decrease in the MI case fatality. In order to obtain a better estimate of the contribution of changing incidence and survivorship to the decreasing mortality rate, we must expand the study from those MIs which are first diagnoses of CHD to all MIs occurring in the local residents. In addition, we propose to extend the coverage from the city of Rochester (current population 55,000) to all of Olmsted County (90,000). Finally, we propose to carry the entire study forward through 1982. Also, all local deaths are being uniformly re-coded to the ICDA 8th revision for the period 1960-1967; this should also be extended to cover 1950-82. Olmsted County, Minnesota, is an ideal community for the studies proposed, since the medical recodes are of uniform high quality, cover the population of the county with excellent case ascertainment, and are already assembled and retrievable by diagnosis.